feat(pygal): implement bubble-packed (#1073)

## Implementation: `bubble-packed` - pygal

Implements the **pygal** version of `bubble-packed`.

**File:** `plots/bubble-packed/implementations/pygal.py`

**Parent Issue:** #992

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20279594554)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/bubble-packed/implementations/pygal.py

@@ -0,0 +1,185 @@
+"""
+bubble-packed: Basic Packed Bubble Chart
+Library: pygal
+
+Uses pygal's XML filter to add packed circle elements.
+Pygal doesn't have native packed bubbles, so we use circle packing algorithm.
+"""
+
+import math
+
+import pygal
+from pygal.etree import etree
+from pygal.style import Style
+
+
+# Data - Department budget allocation (values determine circle size)
+data = [
+    {"label": "Software Development", "value": 450, "group": "Technology"},
+    {"label": "Cloud Infrastructure", "value": 280, "group": "Technology"},
+    {"label": "Data Analytics", "value": 180, "group": "Technology"},
+    {"label": "Security", "value": 120, "group": "Technology"},
+    {"label": "Digital Marketing", "value": 350, "group": "Marketing"},
+    {"label": "Brand & Creative", "value": 220, "group": "Marketing"},
+    {"label": "Events", "value": 150, "group": "Marketing"},
+    {"label": "PR", "value": 90, "group": "Marketing"},
+    {"label": "Facilities", "value": 280, "group": "Operations"},
+    {"label": "HR & Recruiting", "value": 200, "group": "Operations"},
+    {"label": "Legal", "value": 160, "group": "Operations"},
+    {"label": "Admin", "value": 100, "group": "Operations"},
+    {"label": "Enterprise", "value": 380, "group": "Sales"},
+    {"label": "SMB", "value": 250, "group": "Sales"},
+    {"label": "Partners", "value": 170, "group": "Sales"},
+    {"label": "Support", "value": 110, "group": "Sales"},
+]
+
+
+# Circle packing algorithm
+def pack_circles(items, width, height, padding=15):
+    """Pack circles together without overlap using greedy placement."""
+    if not items:
+        return []
+
+    # Scale values to radii (by area for accurate visual perception)
+    max_val = max(item["value"] for item in items)
+    max_radius = min(width, height) * 0.11
+
+    circles = []
+    for item in items:
+        r = math.sqrt(item["value"] / max_val) * max_radius
+        circles.append({"r": r, "item": item, "x": 0, "y": 0})
+
+    # Sort by radius descending for better packing
+    circles.sort(key=lambda c: -c["r"])
+
+    # Place first circle at center
+    cx, cy = width / 2, height / 2
+    circles[0]["x"] = cx
+    circles[0]["y"] = cy
+    placed = [circles[0]]
+
+    # Place remaining circles
+    for circle in circles[1:]:
+        best_pos = None
+        min_dist_from_center = float("inf")
+
+        # Try placing adjacent to each existing circle
+        for existing in placed:
+            for angle_deg in range(0, 360, 8):
+                angle = math.radians(angle_deg)
+                dist = existing["r"] + circle["r"] + padding
+                nx = existing["x"] + math.cos(angle) * dist
+                ny = existing["y"] + math.sin(angle) * dist
+
+                # Check for overlaps
+                valid = True
+                for other in placed:
+                    dx = nx - other["x"]
+                    dy = ny - other["y"]
+                    min_gap = circle["r"] + other["r"] + padding * 0.5
+                    if math.sqrt(dx * dx + dy * dy) < min_gap:
+                        valid = False
+                        break
+
+                if valid:
+                    d = math.sqrt((nx - cx) ** 2 + (ny - cy) ** 2)
+                    if d < min_dist_from_center:
+                        min_dist_from_center = d
+                        best_pos = (nx, ny)
+
+        if best_pos:
+            circle["x"], circle["y"] = best_pos
+        else:
+            circle["x"] = cx
+            circle["y"] = max(c["y"] + c["r"] for c in placed) + circle["r"] + padding
+
+        placed.append(circle)
+
+    return [(c["x"], c["y"], c["r"], c["item"]) for c in placed]
+
+
+# Chart dimensions
+WIDTH = 4800
+HEIGHT = 2700
+
+# Pack circles
+packed = pack_circles(data, WIDTH, HEIGHT)
+
+# Group colors matching pyplots style
+GROUP_COLORS = {"Technology": "#306998", "Marketing": "#FFD43B", "Operations": "#4ECDC4", "Sales": "#FF6B6B"}
+
+# Custom style
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#333",
+    foreground_strong="#333",
+    foreground_subtle="#666",
+    colors=list(GROUP_COLORS.values()),
+    title_font_size=72,
+    legend_font_size=42,
+)
+
+# Create base chart (Pie with no data, just for structure)
+chart = pygal.Pie(
+    width=WIDTH,
+    height=HEIGHT,
+    style=custom_style,
+    title="bubble-packed · pygal · pyplots.ai",
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_at_bottom_columns=4,
+    inner_radius=0,
+    margin=100,
+)
+
+# Add legend entries (empty slices just for legend)
+for group in ["Technology", "Marketing", "Operations", "Sales"]:
+    chart.add(group, [])
+
+
+# XML filter to add packed bubbles
+def add_packed_bubbles(root):
+    """Add packed bubble circles to SVG."""
+    # Create group for bubbles
+    g = etree.SubElement(root, "g")
+    g.set("class", "packed-bubbles")
+
+    for x, y, r, item in packed:
+        color = GROUP_COLORS[item["group"]]
+
+        # Circle element
+        circle = etree.SubElement(g, "circle")
+        circle.set("cx", f"{x:.1f}")
+        circle.set("cy", f"{y:.1f}")
+        circle.set("r", f"{r:.1f}")
+        circle.set("fill", color)
+        circle.set("fill-opacity", "0.85")
+        circle.set("stroke", "#333")
+        circle.set("stroke-width", "3")
+
+        # Tooltip
+        title = etree.SubElement(circle, "title")
+        title.text = f"{item['label']}: ${item['value']}K"
+
+        # Value label for large circles
+        if r > 80:
+            text = etree.SubElement(g, "text")
+            text.set("x", f"{x:.1f}")
+            text.set("y", f"{y:.1f}")
+            text.set("text-anchor", "middle")
+            text.set("dominant-baseline", "middle")
+            text.set("fill", "white")
+            text.set("font-size", f"{int(r * 0.32)}")
+            text.set("font-family", "sans-serif")
+            text.set("font-weight", "bold")
+            text.text = f"${item['value']}K"
+
+    return root
+
+
+chart.add_xml_filter(add_packed_bubbles)
+
+# Render and save
+chart.render_to_png("plot.png")
+chart.render_to_file("plot.html")

plots/bubble-packed/metadata/pygal.yaml

@@ -0,0 +1,23 @@
+# Per-library metadata for pygal implementation of bubble-packed
+# Auto-generated by impl-generate.yml
+
+library: pygal
+specification_id: bubble-packed
+
+# Preview URLs (filled by workflow)
+preview_url: https://storage.googleapis.com/pyplots-images/plots/bubble-packed/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/bubble-packed/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/bubble-packed/pygal/plot.html
+
+current:
+  version: 0
+  generated_at: 2025-12-16T19:10:00Z
+  generated_by: claude-opus-4-5-20251101
+  workflow_run: 20279594554
+  issue: 992
+  quality_score: 91
+  # Version info (filled by workflow)
+  python_version: "3.13.11"
+  library_version: "unknown"
+
+history: []